Production of high crimp, high strength, hollow rayon fibers

Abstract

High crimp, high strength, hollow rayon fibers or filaments which maintain their hollowness after being immersed in water and subsequently dried, and have a crimped configuration such that there is in excess of about 20 crimps per inch, preferably between about 25-30 crimps per inch, are provided by an in-line process whereby a viscose solution containing a blowing agent is extruded into an aqueous acid coagulating bath. The conditions of the process result in hollow filaments that are substantially irreversible since they remain hollow and do not collapse even after repeated washing and drying cycles. The hollow filaments possess high crimp, such as about 25-30 crimps per inch, which will permit ease in carding and blending with other fibers. The high crimp hollow fibers also possess high strength nearly equivalent to that of high wet modulus rayon fibers.

What is claimed is: 
     
       1. A process for producing high crimp, high strength, hollow rayon fibers resistant to collapse after drying and having at least about 20 crimps to the inch, which process comprises spinning a viscose solution containing alkali cellulose, a blowing agent selected from the class consisting of alkali-metal carbonates and alkali-metal bicarbonates, carbon disulfide, in an amount of between about 50 percent and 75 percent by weight of cellulose, and ripened to a Salt Index of from about 6 to 12 cubic centimeters of sodium chloride, into an aqueous acidic coagulating bath containing from about 150 to 300 grams per liter of sodium sulfate, from about 50 to 80 grams per liter of sulfuric acid, and from about 30 to 90 grams per liter of zinc sulfate, and thereafter stretching the resulting hollow fibers by between about 40 and 180 percent. 
     
     
       2. A process in accordance with claim 1, wherein said viscose solution contains cellulose in an amount of from about 6 to 8.0 percent by weight on weight of viscose, alkali-metal hydroxide in an amount of from about 6 to 8 percent on weight of viscose and a viscosity of from about 90 to 140 poises. 
     
     
       3. A process in accordance with claim 1, wherein said viscose solution contains carbon disulfide in an amount of between about 60 and 70 percent by weight of cellulose, and a viscosity of from about 110 to 130 poises. 
     
     
       4. A process in accordance with claim 1, wherein the aqueous acidic coagulating bath is maintained at a temperature of from about 25° to 65° C. 
     
     
       5. A process in accordance with claim 1, wherein the aqueous acidic coagulating bath is maintained at a temperature of between about 35° and 45° C. 
     
     
       6. A process in accordance with claim 1, wherein the blown filaments, after being formed in the aqueous acid coagulating bath, are passed into an aqueous bath comprising between about 5 and 30 grams per liter of sulfuric acid, between about 2 and 20 grams per liter of zinc sulfate and maintained at a temperature of from about 80° to 100° C. 
     
     
       7. A process in accordance with claim 1, wherein the blowing agent is a member selected from sodium carbonate and sodium bicarbonate. 
     
     
       8. A process in accordance with claim 1, wherein the blowing agent is present in an amount of between about 3.5 percent and 4.5 percent based on weight of cellulose. 
     
     
       9. A process in accordance with claim 1, wherein said viscose solution contains between about 6 and 8.0 percent by weight of cellulose, between about 6 and 8 percent by weight of alkali-metal hydroxide, between about 50 and 75 percent by weight of carbon disulfide, based on weight of cellulose, between about 3 and 5 percent by weight of a member selected from an alkali-metal carbonate and bicarbonate as a blowing agent, said viscose solution having a viscosity of between about 90 and 140 poises and said aqueous acidic coagulating bath contains between about 30 and 80 grams per liter of zinc sulfate, between about 150 and 300 grams per liter of sodium sulfate and between about 50 and 80 grams per liter of sulfuric acid, and stretching the resulting hollow rayon fibers by between about 40 and 180 percent. 
     
     
       10. A process in accordance with claim 1, wherein said viscose solution contains about 7 percent by weight of cellulose, between about 6.5 and 7.5 percent by weight of alkali-metal hydroxide, between about 60 and 70 percent by weight of carbon disulfide, based on weight of cellulose between about 3.5 and 4.5 percent by weight of a member selected from an alkali-metal carbonate and bicarbonate as a blowing agent, said viscose solution having a viscosity of between about 110 and 130 poises and said aqueous acidic coagulating bath contains between about 40 and 70 grams per liter of zinc sulfate, between about 240 and 280 grams per liter of sodium sulfate and between about 60 and 70 grams per liter of sulfuric acid, and stretching the resulting hollow rayon fibers between about 90 and 100 percent.